Air Temperature and Precipitation

This section will focus on local and regional air temperature and precipitation patterns, and compare these values to historical conditions. The winter season was generally cooler than average (as is common during La Nina seasons), and saw near-normal precipitation and snowpack levels. Conditions changed abruptly near the end of April. This spring and summer have been warm (or hot) and exceptionally dry.

The maps below show temperature anomalies and percent of normal precipitation for Western Canada in June, July, and August. Warm and dry conditions are a common theme for most of British Columbia for the past few months. The local temperature anomalies are not captured as well in this product, so we’ll look a little more closely at watershed conditions below.

Fig. 5 June-July-August (JJA) Temperature Anomalies for Western Canada

Fig. 6 June-July-August (JJA) Percent of Normal Precipitation for Western Canada

The table below shows monthly average air temperature and precipitation data for the Lower Capilano Watershed. May is certainly a standout month with average temperatures almost 4 degrees warmer than normal, but temperatures have consistently been warmer than normal since late April. Only 144 mm of rain has fallen since April 24th, which is around 35% of normal for this period.

Month	Mean Temp (°C )	Temp Anomaly (°C )	Precip (mm)	Precip % Normal
January	3.5	+0.4	318	87
February	1.8	-1.0	333	145
March	4.2	-0.6	118	35
April	6.2	-1.2	315	159
May	15.4	+3.7	19	15
June	16.5	+1.3	48	45
July	19.4	+1.8	44	96
August	19.0	+1.3	42	44

Air Temperatures

The plot below shows the average daily temperature for 2023 (red line) compared to normals (gray shaded area) and the range of max and min (blue shaded area). New high and low temperature records are also plotted with red and blue dots. The sudden change in temperatures at the end of April is very clear. Seventeen new daily high temperature records have been set in 2023 so far, with nine high temperature records set in May alone.

Hottest Day of the year

The hottest recorded temperature so far this year was on August 13th. The daytime high reached 35.3 degrees in the Coquitlam Watershed

Precipitation

The plot below shows the accumulated precipitation in the Lower Capilano Watershed in 2023. Last year is also shown in dark blue, and other years between 2003 and 2021 are shown with lighter shades of blue. Average annual accumulated precipitation is shown with the black dashed line.

The winter was marked by near normal precipitation, with the heaviest rain in February and the first half of April. It has been exceptionally dry since late April. Only 144 mm of rain has fallen since April 24. On average, the lower Capilano Watershed typically sees around 375 mm of rain between May 1 and August 31.

We’ll take a closer look at drought in the next section.

Dry Spells!

33 days (May 7 - June 9), and 25 days (June 23 - July 18)

Note: Only 0.5 mm of rain fell in 32 days between June 22 and July 24

Standardized Precipitation Evapotranspiration Index

The Standardized Precipitation Evapotranspiration Index (SPEI) is a multi-scalar drought monitoring index based on climatic data. It’s useful in determining the onset, duration, and magnitude of drought conditions, and captures the main impact of increased temperatures on water demand.

For this report, the SPEI is calculated a 3-month intervals. This is useful for analyzing seasonal drought in the Lower Mainland. Values that fall between 1.0 and -1.0 are considered normal, values below -1.0 highlight dry conditions (red), and values above 1.0 are wet (blue). Each bar in the plot below represents the SPEI value for the previous 3 months. As we can see, conditions have been dry-to-very dry for the past two summers. We’ll examine this drought more closely in the next section.